In taking a quick look at the schematic, it looks to me like if the headphone out is working, then little stands in the way of the main outs being there. Looks like there is a relay mute circuit and normal build out resistors.
If you had a bad cable or did something outboard that pulled high current you could maybe have just a simple resistor opened. But more likely would be a relay failure. If that's what it is, you might be able to lightly whack the relay and hear burps of audio come through it. Technical troubleshooting taps on it only. That's only for properly licensed tech's to do of course!
The year of the 10th Carverfest! Be there at CF2016!